Air purifying filters typically do not have an unlimited service life. End users of air purifying devices must manage cartridge change-out using objective information, data, or an end of service life indicator (ESLI). ESLIs can provide important safety information to users of an air purifying apparatuses, particularly where the purifying device is being used to remove toxic gases from the air being breathed. Commonly used approaches to ESLI include passive and active solutions. Active solutions often involve the use of electronic chemical sensors that are integrated into the sorbent bed of the filter. Placing chemical sensors within the sorbent bed is problematic, however, because the sensors can undesirably disturb air flow in the filter. As a result, the sensor may not detect actual impurity concentration for a majority of the air stream, which can result in false signals. In addition, the presence of the sensor inside the adsorbent bed may adversely affect the air purification outcome and results in shorter service life time of the filter cartridge.
Furthermore, an embedded sensor approach requires that the sensor be disposed along with the cartridge when the service life of the cartridge ends, which greatly increases costs. Embedding a sensor in the sorbent bed also can increase the chance of improper bed packing. Further, it may be technically challenging to mount multiple sensors at various bed locations.
Accordingly, there is a need for an improved sorbent bed-embedded sensor design for use in air purifying filter apparatuses.